Xerographic development control apparatus

ABSTRACT

Apparatus for controlling the introduction of magnetizable developer material to a plurality of magnetic developing rollers for effecting the development of latent electrical charges selectively retained on a support surface in image configuration. The developing apparatus is continually operable with image development being effected by gating developer material to the magnetic developing rollers or recirculating the developer material in the developer apparatus removed from the effective magnetic field of the developing rollers.

United States Patent [111 3,608,522

[72] inventor James R. Davidson 3,327,852 6/1967 Mortsell 209/219 Rochester, N.Y. 3,367,306 2/1968 Lawes et a1 I 18/637 [21] Appl. No. 830,238 3,472,205 10/1969 Tsuchiya et a1 1 17/1 7.5 X

[ Filed June 4, 1969 OTHER REFERENCES [45] patfmted i g 1971 IBM Technical Disclosure Bulletin, Medley Development [73] Asslgnee orponmon of Electrostatic images," Vol. 2. No. 2, (Aug. 1959) pp. 4, 5

Rochester, N.Y.

[54] XEROGRAPHIC DEVELOPMENT CONTROL 623, 602, 603, 636', 198/41; 117/175, 37 L; 346/74'ES, 74 M, 74 MP; 209/219, 216

[56] References Cited UNITED STATES PATENTS 2,745,549 5/1956 Spodig 209/219 3,081,737 '3/1963 Frantz et al. 118/637 3,113,042 12/1963 Hall 118/637 3,238,920 3/1966 Fowlie et a1. 118/637 X Copy 343/74 ES IBM Technical Disclosure Bulletin, Cross et al. Magnetic Brush Developer," Vol. 9, No. 9, (Feb. 1967) pp. 1090, 1091 Copy 346/74 ESX Primary Examiner-Morris Kaplan Attorneys-James J. Ralabate, Norman E. Schrader and Bernard A. Chiama ABSTRACT: Apparatus for controlling the introduction of magnetizable developer material to a plurality of magnetic developing rollers for effecting the development of latent electrical charges selectively retained on a support surface in image configuration. The developing apparatus is continually operable with image development being effected by gating developer material to the magnetic developing rollers or recirculating the developer material in the developer apparatus removed from the effective magnetic field of the developing rollers.

PATENIEUsEP2s|9n 3150 522 SHEET 1 [IF 4 INVENTOR. JAMES R. DAVIDSON BY 0. ATTORNE FIG. 1

XEROGRAPI-IIC DEVELOPMENT CONTROL APPARATUS BACKGROUND OF THE INVENTION This invention relates to the development of electrostatic latent images and, in particular, to an apparatus for controlling the development of electrostatic latent images in a continuously operable developing unit.

More specifically, this invention relates to a control mechanism for e fiecting the introduction of material to develop an electrostatic latent image or to recirculate the developer material within the developer apparatus to eliminate development characteristics resulting from localized developer conditions.

In the development of electrostatic latent images by the application of electrostatic toner powder, for example, of the type disclosed in Carlson U.S. Pat. No. 2,940,934, utilized with development methods such as cascade or magnetic brush development which are well known in the art, certain advantages and improvements in the developing of the latent images would accrue if the developer unit is continuously operating. Continuous operation of the developing apparatus would enhance intermixing of the developer materials to maintain the proper triboelectric bond between the electroscopic toner powder and the carrier material and minimize,

tinuous application of developer material to the latent image.

would not create a problem if the latent image is to be developed solely by electroscopic toner powder of one color, but creates additional problems when utilized in a multicolor xerographic reproducing system.

In reproducing a multicolored original document, it is, desirable to create a series of electrostatic latent images which have been created in response to a sequential color separation of the multicolored original document. This series of latent images is rendered visible by the mutually exclusive development effected by a plurality of developing units, each unit applying a separate colored electroscopic toner powder in response to the color separated latent image. The series of developed images is then transferred to a suitable support medium whereat they form a reproduction of the multicolored original document.

While it would be possible to effect development of the series of latent image by any well known developing method, for example, cascade development, size limitations of the reproducing machine made a compact development system, such as magnetic brush development, desirable.

Furthermore, as the speed of the reproducing machine has increased, it has become necessary that the development unit operate continuously to minimize time delays incurred in development of the latent image. In addition, since reproduction of the multicolored original document is effected by the mutually exclusive operation of one of a plurality of developing units each utilizing a separate color of electroscopic toner powder to develop one of the series of color separated latent images, the development unit must be continuously operated without effecting development of all electrostatic latent images passing adjacent to the development unit.

SUMMARY OF THE INVENTION Therefore, it is an object of this invention to improve apparatus for developing electrostatic latent images.

Another object of this invention is to control the development of electrostatic latent images in continuously operating developing apparatus.

A further object of this invention is to effect and terminate the development of the electrostatic latent image moving relative to the development unit by controlling the introduction of the developer material to the development unit.

These and other objects are attained in accordance with the present invention wherein there is provided a gating or bridging system positioned adjacent the development units to control the introduction of developing material or to recirculate the developing material within the developer housing.

Means are provided to cross-mix the developer material to eliminate development defects and to move the developer material from a sump portion of the developer housing too the control gate.

DESCRIPTION OF THE DRAWINGS Further objects of this invention, together with additional features contributing thereto and advantages accruing therefrom, will be apparent from the following description of one embodiment of the invention when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a mechanical schematic of an automatic xerographic reproducing machine utilizing the invention of this application;

FIG. 2 is an enlarged end view of one of the developing units of the reproducing apparatus illustrated in FIG. 1;

FIG. 3 is an enlarged end view of the developing apparatus shown in FIG. 2 with portions removed to better illustrate the features thereof;

FIG. 4 is a front perspective view of the developing apparatus to better illustrate the developing rollers and the gating apparatus which controls development of the latent electrostatic image and recirculation of the developer material within the developer housing;

FIG. 5 is an enlarged section of a portion of the developing roller to better illustrate the mounting thereof;

FIG. 6 is a rear perspective view of the developing apparatus to better illustrate the mechanism for intermixing the developer material and elevating it to the developing rollers; and

FIG. 7 is a front perspective mechanical schematic of the rotational movement of the development rollers and the operation of the control gate apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1, there is illustrated a cross section mechanical schematic of an automatic xerographic reproducing machine utilizing this invention. As in all electrostatographic systems, illustrated by the xerographic reproducing machine shown, a light image of a document to be reproduced in projected 3 onto a photosensitive surface 1 to form a latent electrostatic image thereon. Thereafter, the latent image is developed 4 to form an electroscopic toner powder image in the configuration of the latent image on the photoreceptor surface. The powder image may then be transferred 5 to a support material to which it may be permanently fixed as by heat fusing, or the toner powder may be permanently affixed to the photoreceptive surface depending on the method of electrostatographic imaging employed as is well known in the art.

Referring now to FIGS. 2 and 4, the developing apparatus 50 extends the width of the photoreceptor l and is substantially enclosed except for an opening adjacent the photoreceptor whereat development of the latent electrostatic image is effected and an opening 11 upon which a toner powder dispenser 10 is positioned to replenish the toner depleted from the developer mixture during development of the electrostatic images. Within the housing of the developer apparatus there is a pump 51 at the lowermost portion of the housing containing developer material comprising magnetizable carrier material and colored electroscopic toner particles. The toner particles are many times smaller than the carrier material and, due to a triboelectric relationship therebetween, substantially uniformly coat the carrier material.

The developing apparatus 50 is positioned within the automatic xerographic reproducing machine adjacent to the photoreceptor l by suitable brackets and braces 45 appropriately secured to the developing apparatus and the frames of the machine. A suitable mounting 12 is provided on the top of the developing apparatus between cover plates 52 and 53 to position and retain the toner powder dispenser 10.

Development of the electrostatic laten image is effected by a blanket of developing material formed between a pair of adjacent magnetic rollers 70 and 80 positioned such that their magnetic force fields intersect to effect formation of a blanket of developing material upon the rollers 70 and 80, and in the space therebetween adjacent the photoreceptor 1. The magnetic rollers 70 and 80 comprise outer cylinders 71 and 81, respectively, of a nonmagnetic material such as aluminum extending the width of the developer housing with elongated bar magnets 72 and 82, respectively, extending nearly the full length of each cylinder. The bar magnets 72 and 82 are each supported, for example on a ferromagnetic bar 73 having rod 74 secured to each end, as by welding, and securely fastened in mounting blocks 75 appropriately secured to side frame plates 54) of the developer apparatus. The outer cylinders 71 and 81 of nonmagnetic material are each mounted for rotation within the developer housing by means of suitable bearing surfaces 76 carried by the side frame plates 54 of the developer housing (FIG. One end of the cylinder is enclosed by a cap 77 having a central opening therein, through which the rod portion 74 passes, and is rotatably supported thereabout in the frame plate 54 by the bearing 76. The driven end is enclosed by an end cap 78 rotatably supported in suitable bearings in the side frame plate 54 and having a drive gear 89 secured thereto to effect rotation of each cylinder. The rotational drive for all other rotary components of the developing apparatus 50 is derived from drive gear 89 by means of a suitable timing belt (not shown) engaging suitable drive connections on each component. In this manner the outer cylinders may be rotatably driven about the stationary elongated bar magnets 72 and 82. The polar orientation of the elongated bar magnets is indicated in FIG. 3 and is arranged such that the magnetic force fields project through the walls of the nonmagnetic cylinders 71 and 81 to form the magnetizable carrier material into a brushlike configuration in a manner well known in the art.

As best shown in FIGS. 3 and 4, the peripheral walls of the cylinders 71 and 81 are positioned in closely spaced relationship adjacent to one another. During a development cycle when both cylinders are rotating in synchronism about their respective stationary bar magnets 72 and 82, the brush bristles produced by action of the magnetic field emanating from the magnets acting upon the magnetizable carrier material will form on the upper region of the cylinder 71 within the magnetic field emanating from magnets 72 and the under surface of the electrostatic image bearing photoreceptor 1. These bristles are formed during the developing cycle, and are produced by the magnetic field from the bar magnets 72. When the bristles are moved by the cylinders 71 out of the influence of magnet 72 beyond the closest distance between the photoreceptor 1 and the cylinder 71, they are attracted by the greater magnetic field of the magnet 82 which is stronger at this point than the diminished strength of the magnetic field attributed to the magnet 72. The developer material is carried therealong during rotation of the cylinder 81 until the material reaches a point beyond the development zone whereat the magnet field is diminished and the carrier material and toner particles drop off the cylinder 31 and back into the sump portion 51 of the developer apparatus. A suitable stripping mechanism such as a nonmagnetizable doctor blade 96 may be utilized to ensure that the magnetizable developer material is removed from the cylinder 81.

During movement of the developer material through the development zone between the two cylinders '71 and 81, the magnetizable developer material is in the form of a blanket extending the entire distance (FIG. 3) between the two cylinders -and in contact with the photoreceptor 1. Therefore, the width of the development zone is larger than the sum of the individual development zones for either of the magnetic rollers 71 or 81.

After the developer material has effected development of the latent image on the photoreceptor surface, the material is removed from he cylinder 81 and passed to the sump portion 51 of the developer apparatus. A vaned churn 20 is rotatably mounted within the side frame plates 54 of the developer apparatus by suitable bearings and functions to intermix the developer material to eliminate development defects characteristic of poor intermixing of the developer material. The churn comprises a plurality of spaced vanes 21 positioned in a herringbone configuration and carried by spacers 22 which are appropriately secured to the vanes as by welding and secured to the shaft 23. The shaft 23 is rotatably mounted in suitable bearing surfaces in the side frame plates 54 and driven by means ofa gear (not shown) suitably secured to one end of the shaft 23 and engaging a suitable drive system. The herringbone configuration of the vanes 21 conveys the developer material from the outer edges of the developer sump 51 to the center portion to cross-mix the developer material to eliminate problems of localized toner starvation of the carrier material. In addition, the vanes 21 are spaced from one another on the spacers 22 thereby allowing the developer material to fall through the spaces between individual vanes as the material is lifted during rotation of the churn 20.

As the material is cross-mixed and interchanged to eliminate development defects due to the relationship between the carrier material and the toner powder, and to maintain the proper triboelectric relationship therebetween, it is lifted by the vanes into the magnetic field of the pickoff or conveying roller 61) (FIGS. 3, 4 and 7) which is rotatably mounted within the side frame plates 54 of the developer housing in a manner previously described with reference to the magnetic rollers 70 and 80. This roller is formed in the same manner as those previously described in that a stationary bar magnet 62 is employed suitably secured in the side frame plates 54, with an outer cylinder of nonmagnetic material 61 rotatably supported thereabout. The developer material is at tracted from the elevating vanes 21 by the magnets 62 to the surface of cylinder 61 to be forwarded to the developing rollers (70 and or to be returned to the sump portion as controlled by the operation ofa developer gate or bridge 30.

The gate 30 (FIG. 2, 3, 4 and '7) comprises a generally L- shaped baffle plate of nonmagnetic material 31 secured to a shaft 32 which is rotatably journaled in the side frame plates 54! by suitable bearings. One end of the shaft 32 extends through the side frame plate to be engaged by a yoke 33 which is secured to the shaft at one end and to the plunger 34 of a solenoid SOL-1 supported on the side frame plate 54 by a suitable bracket 55.

The solenoid is positioned such that upon actuation thereof the plunger will pivot the gate in a clockwise position as shown in FIG. 3 raising the contact edge 31a of the gate from the surface of the cylinder 61 to convey the magnetizable developer material below the edge of the gate out of the influence of the magnetic field of magnet 62 to fall back into the sump potion 51 of the developer unit. When the solenoid is deactuated the plunger will rotate the gate in a counterclockwise direction as seen in FIG. 3 such that the edge 31a of the gate will engage the surface of the cylinder 61 thereby forming a bridge between the surface of the cylinder 61 and the cylinder 71 of the developing roller 70. The developer material will be attracted from the vanes 21 by the pickoff cylinder 60, removed from the cylinder 61 by the scraping action of the edge 31a of a gate 30, and will flow across the gate into the influence of the magnetic developing unit 70 whereat the developer material will be conveyed into the developing zonev In this manner, the vanes 21 may be continuously operating to intermix the developer material and elevating it into the influence of the magnetic field from the pickoff roller 60, even though the developing unit 50 is not being utilized for development of the latent electrostatic image passing adjacent to the developing zone of rollers 70 and 80.

Such a system for gating the flow of developer material to the development units becomes especially important in a color hum-1 m...

development system since it is desired to effect mutually exclusive development of the latent electrostatic image by one of plurality of development units, each development unit containing an electroscopic toner powder of a separate color. By utilizing a gating apparatus in this manner the developer mixture may be continually intermixed to maintaig a proper triboelectric relationship between the carrier material and the toner powder and to eliminate development defects even though the unit is not being utilized to effect development of the latent electrostatic image passing adjacent thereto.

While there has been shown and described on embodiment of the invention, it is intended that the invention be not limited to the exact form shown and described or to anything less than the whole of the invention as set forth in the appended claims.

1. Apparatus for controlling the introduction oflmagnetizable developer material to a magnetic-field-emitting developing unit for effecting the development of a support medium having electrical charges selectively retained in a latent image configuration comprising magnetic-field-emitting conveying means positioned adjacent a magnetic-field-emitting developing unit and removed from the latent image bearing support medium to convey magnetizable developer material to the magnetic field emitted by the developing unit,

gating means positioned between said magnetic-fieldemitting conveying means and the developing unit positionable to control the conveying of developer material to the magnetic field emitted by the developing unit for effecting development of the latent image,

said gating means includes a bridging member actuable to contact said magpetic-field-emitting conveying means to remove the developer material conveyed thereby for introducing the developer material to the magnetic field emitted from said developing unit,

said bridging member is actuable out of contact with said magnetic-field-emitting conveying means to pass the developer material adjacent said bridging member and out from contact with the effective magnetic field emitted from said conveying means into a developer sump.

2. The apparatus of claim 1 wherein said magnetic fieldemitting-conveying means positioned adjacent a magneticfield-emitting developing unit includes a pickoff roller comprising a nonmagnetic cylinder rotatably supported about a magnet.

3. The apparatus of claim 2 wherein said gating means positioned between said conveying means and the developing unit comprises a baffle plate pivotally supported between said pickoff roller and said magnet-field-emitting developing unit actuable into and outfrom contact with said pickoff roller to control the conveying of developer material to the support surface in response to the pivoting of said baffle plate into contact with said pickoff roller.

4. The apparatus of claim 3 wherein said baffle plate is pivotally actuable in response to the energization of a solenoid.

5. The apparatus of claim 3 wherein said baffle plate is formed from a nonmagnetic material. 

2. The apparatus of claim 1 wherein said magnetic field-emitting-conveying means positioned adjacent a magnetic-field-emitting developing unit includes a pickoff roller comprising a nonmagnetic cylinder rotatably supported about a magnet.
 3. The apparatus of claim 2 wherein said gating means positioned between said conveying means and the developing unit comprises a baffle plate pivotally supported between said pickoff roller and said magnet-field-emitting developing unit actuable into and out from contact with said pickoff roller to control the conveying of developer material to the support surface in response to the pivoting of said baffle plate into contact with said pickoff roller.
 4. The apparatus of claim 3 wherein said baffle plate is pivotally actuable in response to the energization of a solenoid.
 5. The apparatus of claim 3 wherein said baffle plate is formed from a nonmagnetic material. 